I have a 93 400 SEL. When operating a/c system. Cold air blows from center vents and hot air blows from side vents. Have to close side vents to eliminate hot air. Dealer originally replace A/C control panel ($1,449). Day later problem occurred again. Replaced heater value/monovalve ($839.93). Did a/c control panel really need replacing? Have I paid for misdiagnosis?